Mizzen on a yawl:

It is a mooted question among yawlsmen as to whether the mizzen is of use or not when going dead before the wind. If you can wing it—that is, get the boom on the opposite side to that of the mainboom—it is, as it makes a boat steer steadier. But if it is off on the same side as the mainsail it is doubtful if it helps the speed. I have tried the experiment repeatedly and cannot find that it makes any difference in a strong breeze; but it does help in light airs. In a strong wind the boat will do better with the mizzen stowed, is my opinion.